1. Field of the Invention
The present invention relates to a solid-state image sensor, a range finder using the solid-state image sensor and imaging devices using the range finder, such as a digital still camera and a digital video camera.
2. Description of the Related Art
In a digital still camera or video camera, a distance-detecting technology for AF (automatic focusing) is known. Regarding such a ranging technology for AF, Japanese Patent Application Laid-Open No. 2009-158800 has proposed a solid-state image sensor with a ranging function given to some of pixels thereof so as to conduct detection by a phase difference method. This phase difference method is a method in which light images passed through different regions on a pupil of an imaging optical system are compared to detect an object distance using triangulation by a stereo image. According to this system, there is no need to move a lens for measuring an object distance unlike the conventional contrast system, so that high-speed and high-precision automatic focusing becomes feasible. In addition, upon taking moving images, real-time AF becomes feasible. Japanese Patent Application Laid-Open No. 2009-158800 discloses a solid-state image sensor provided with a waveguide on a plurality of photoelectric conversion portions as a structure of a ranging pixel. Light images passed through different regions on the pupil of the imaging optical system are coupled with different two waveguides using a microlens having an imaging plane at an end surface of the waveguide, whereby they can be guided to different photoelectric conversion portions to measure the object distance.
According to the solid-state image sensor disclosed in Japanese Patent Application Laid-Open No. 2009-158800, however, ranging precision may be deteriorated in some cases when there are a lot of light fluxes incident at a large incident angle on a ranging pixel in a peripheral portion of the solid-state image sensor or in a solid-state image sensor with respect to a luminous imaging optical system. The light flux incident at the large incident angle on the ranging pixel is easily coupled with a higher-order eigenmode in a waveguide and propagates at a guided mode in which an electric field distribution spread in the waveguide to reach a plurality of photoelectric conversion portions in the pixel. Therefore, it is difficult to selectively guide light having passed through each pupil region to different photoelectric conversion portions, and so ranging precision may be deteriorated in some cases.